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Mitsubishi NF-S Series Technical Notes

Moulded case circuit breakers
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ADVANCED AND EVER ADVANCING
MOULDED CASE CIRCUIT BREAKERS
TECHNICAL NOTES
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Summary of Contents for Mitsubishi NF-S Series

  • Page 1 ADVANCED AND EVER ADVANCING MOULDED CASE CIRCUIT BREAKERS TECHNICAL NOTES...

  • Page 2: Table Of Contents

    We have the pleasure of providing all our customers with the technical information for Mitsubishi moulded case circuit breakers. This indicates the fundamental data of our circuit breakers regarding the applicable standards, constructional principles, and operational performances. Please refer to the catalogue of our circuit breakers for details of specifications.

  • Page 3: Introduction

    Manufacture commences of short-time- delayed breakers. Since production began in 1933 many millions of 1969 Production and sale of first residual cur- Mitsubishi ACBs, MCCBs and MCBs have been sold rent circuit breakers. throughout many countries. 1970 170kA breaking level ‘permanent power fuse’...

  • Page 4: Features

    80% (compared with Mitsubishi’s 100AF). The passing energy I t de- Movable contact creases to about 65% (compared with Mitsubishi’s Pressure 100AF). The smaller breaking space has led to an Movable improved function, a smaller size, and a standardiza-...

  • Page 5: Digital Etr

    2.2 Digital ETR (Electronic Trip Relay) Processing of the digital ETR Mitsubishi’s electronic MCCBs are equipped with a digital ETR to enable fine protection. The digital ETR contains Mitsubishi’s original double IC (8 bit microcomputer and custom-IC). Digital detection of the effective value Electronic devices such as an inverter distort the cur- rent waveform.
  • Page 6 2.3 Equipment of High Technology Advanced Technology Series Type ISTAC Analog-ETR Digital-ETR NF30-SP NF50-HP NF50-HRP NF60-HP NF100-SP NF100-HP NF100-SEP NF100-HEP NF160-SP NF160-HP NF250-SP NF250-HP NF250-SEP NF250-HEP NF-S NF400-SP NF400-SEP NF400-HEP NF400-REP NF630-SP NF630-SEP NF630-HEP NF630-REP NF800-SEP NF800-HEP NF800-REP NF1000-SS NF1250-SS NF1600-SS NF50-CP NF60-CP...

  • Page 7: Construction And Operation

    The primary components are: a switching mechanism, an automatic tripping device (and manual trip button), contacts, an arc-extinguishing device, terminals and a molded case. Arc-Extinguishing Device Mitsubishi MCCBs feature excel- lent arc-extinguishing perfor- mance by virtue of the optimum combination of grid gap, shape, and material.
  • Page 8 3.2 Switching Mechanism Spring tension line The ON, OFF and TRIPPED conditions are shown in ON to OFF dead-point line Fig. 3.2. In passing from ON to OFF, the handle ten- sion spring passes through alignment with the toggle Toggle link Spring link (“dead point”...
  • Page 9 Automatic Tripping Devices Thermal-Magnetic Type (100~630A Frame) 1. Time-Delay Operation Armature Bimetal Trip bar An overcurrent heats and warps the bi- Heater metal to actuate the trip bar. Latch 2. Instantaneous Operation If the overcurrent is excessive, the amature is attracted and the trip bar ac- tuated.
  • Page 10 Table 3.1 Comparison of Thermal-Magnetic, Hydraulic-Magnetic and Electronic Types Item Thermal-magnetic type Hydraulic-magnetic type Electronic type Negligible effect Operating current is affected by ambient Affected only to the extent that the damp- temperature (bimetal responds to absolute ing-oil viscosity is affected. temperature not temperature rise).
  • Page 11 Induced flux mize deterioration of contacts and adjacent insulat- ing materials. In Mitsubishi MCCBs a simple, reliable, Grid and highly effective “de-ion arc extinguisher,” consist- ing of shaped magnetic plates (grids) spaced apart in an insulating supporting frame, is used (Fig.

  • Page 12: Characteristics And Performance

    The figures reflect all poles tested to- the former. The necessary data for establishing the gether for 130% tripping, and 105% non-tripping. required compatibility is provided in the Mitsubishi Within the range of the long-delay-element (thermal MCCB sales catalogues.

  • Page 13: Effects Of Mounting Attitudes

    At commercial frequencies the characteristics of The instantaneous trip current will gradually in- Mitsubishi MCCBs of below 630A frame size are vir- crease with frequency, due to reverse excitation by tually constant at both 50Hz and 60Hz (except for the eddy currents.

  • Page 14: Switching Characteristics

    0.5~1.5µsec and a tail-length of 32~48µsec. The volt- In addition to the requirements of the various interna- age is applied between line and load terminals (MCCB tional standards, Mitsubishi MCCBs also have the off), and between live parts and ground (MCCB on). impulse-voltage withstand capabilities given below (Table 4.4).

  • Page 15: Circuit Breakers Selection

    5. CIRCUIT BREAKER SELECTION 5.1 Circuit Breaker Selection Table Following Table shows various characteristics of each breaker to consider selection and coordination with upstream devices or loads. Characteristics Standard : Standard characteristics MCCBs Low-inst : Low-inst. MCCBs for Discrimination When a power fuse (PF) is used as a high-voltage protector, it must be coordinated with an MCCBs on the secondary side.
  • Page 16 CIRCUIT BREAKER SELECTION TABLE Frame (A) Type NF30-CS NF30-SP NF50-CP Rated current In (A) 3, 5, 10, 15, 20, 30 10, 15, 20, 30, 40, 50 3, 5, 10, 15, 20, 30 Rated insulation voltage Ui (V) AC – – –...
  • Page 17 Frame (A) Type NF50-HP NF60-CP Rated current In (A) 10, 15, 20, 30, 40, 50 10, 15, 20, 30, 40, 50, 60 Rated insulation voltage Ui (V) AC – – 690V AC Breaking 7.5/4 2.5/1 500V capacity (kA rms) 10/5 2.5/1 440V IEC60947-2...
  • Page 18 Frame (A) NF60-HP Type NF100-CP NF100-SP Rated current In (A) 10, 15, 20, 30, 40, 50, 60 50, 60, 75, 100 15, 20, 30, 40, 50, 60, 75, 100 Rated insulation voltage Ui (V) AC 690V – – – AC Breaking 500V 7.5/4 7.5/4...
  • Page 19 Frame (A) Type NF100-CP T/A NF50-HRP NF100-SP T/A 15 ~ 20, 20 ~ 25, 25 ~ 40 15 ~ 20, 20 ~ 25, 25 ~ 40 Rated current In (A) 15, 20, 30, 40, 50 40 ~ 63, 63 ~ 80, 80 ~ 100 40 ~ 63, 63 ~ 80, 80 ~ 100 Rated insulation voltage Ui (V) AC 690V...
  • Page 20 Frame (A) Type NF100-HP NF100-HP T/A NF100-RP 15 ~ 20, 20 ~ 25, 25 ~ 40 Rated current In (A) 15, 20, 30, 40, 50, 60, 75, 100 15, 20, 30, 40, 50, 60, 75, 100 40 ~ 63, 63 ~ 80, 80 ~ 100 Rated insulation voltage Ui (V) AC 690V –...
  • Page 21 Frame (A) Type NF100-UP NF100-SEP NF100-HEP Rated current In (A) 15, 20, 30, 40, 50, 60, 75, 100 15 ~ 20, 30 ~ 50, 60 ~ 100 15 ~ 20, 30 ~ 50, 60 ~ 100 Rated insulation voltage Ui (V) AC 690V 10/5 –...
  • Page 22 Frame (A) Type NF160-HP NF160-SP NF160-SP T/A Rated current In (A) 125, 150, 160 100 ~ 125, 125 ~ 160 125, 150, 160 Rated insulation voltage Ui (V) AC 690V – – AC Breaking 500V 15/8 15/8 30/8 capacity (kA rms) 440V 25/13 25/13...
  • Page 23 Frame (A) NF250-CP T/A Type NF160-HP T/A NF250-CP 100 ~ 125, 125 ~ 160 Rated current In (A) 100 ~ 125, 125 ~ 160 125, 150, 175, 200, 225, 250 150 ~ 200, 200 ~ 250 Rated insulation voltage Ui (V) AC –...
  • Page 24 Frame (A) Type NF250-SP NF250-SP T/A NF250-HP 100 ~ 125, 125 ~ 160 Rated current In (A) 125, 150, 175, 200, 225, 250 125, 150, 175, 200, 225, 250 150 ~ 200, 200 ~ 250 Rated insulation voltage Ui (V) AC –...
  • Page 25 Frame (A) Type NF250-HP T/A NF225-RP NF225-UP 100 ~ 125, 125 ~ 160 Rated current In (A) 125, 150, 175, 200, 225 125, 150, 175, 200, 225 150 ~ 200, 200 ~ 250 Rated insulation voltage Ui (V) AC – 10/5 690V AC Breaking...
  • Page 26 Frame (A) NF250-SEP NF250-HEP Type Rated current In (A) 125-250 125-250 Rated insulation voltage Ui (V) AC 690V – AC Breaking 500V 15/8 30/8 capacity (kA rms) 440V 25/13 50/13 IEC60947-2 400V 30/15 50/13 Icu/Ics 230V 50/25 100/25 Number of poles Standard Electronic trip relay Electronic trip relay...
  • Page 27 Frame (A) 400A NF400-SEP Type NF400-CP NF400-SP 200 ~ 400 Rated current In (A) 250, 300, 350, 400 250, 300, 350, 400 adjustable Rated insulation voltage Ui (V) AC 10/10 10/10 690V – AC Breaking 30/30 30/30 500V 15/8 capacity (kA rms) 42/42 42/42 440V...
  • Page 28 Frame (A) 400A Type NF400-HEP NF400-REP NF400-UEP 200 ~ 400 200 ~ 400 200 ~ 400 Rated current In (A) adjustable adjustable adjustable Rated insulation voltage Ui (V) AC 10/10 15/10 35/35 690V AC Breaking 50/50 70/35 170/170 500V capacity (kA rms) 65/65 125/63 200/200...
  • Page 29 Frame (A) 630A Type NF630-CP NF630-SP NF630-SEP 300 ~ 630 Rated current In (A) 500, 600, 630 500, 600, 630 adjustable Rated insulation voltage Ui (V) AC – 10/10 10/10 690V AC Breaking 18/9 30/30 30/30 500V capacity (kA rms) 36/18 42/42 42/42...
  • Page 30 Frame (A) 630A Type NF630-HEP NF630-REP NF630-UEP 300 ~ 630 300 ~ 630 300 ~ 630 Rated current In (A) adjustable adjustable adjustable Rated insulation voltage Ui (V) AC 15/15 35/35 690V 20/15 AC Breaking 170/170 50/50 70/35 500V capacity (kA rms) 65/65 125/63 200/200...
  • Page 31 Frame (A) 800A Type NF800-CEP NF800-SEP NF800-HEP 400 ~ 800 400 ~ 800 400 ~ 800 Rated current In (A) adjustable adjustable adjustable Rated insulation voltage Ui (V) AC – 10/10 15/15 690V AC Breaking 18/9 30/30 50/50 500V capacity (kA rms) 36/18 42/42 65/65...
  • Page 32 Frame (A) 800A Type NF800-REP NF800-UEP 400 ~ 800 400 ~ 800 Rated current In (A) adjustable adjustable Rated insulation voltage Ui (V) AC 20/15 35/35 690V AC Breaking 70/35 170/170 500V capacity (kA rms) 125/63 200/200 440V IEC60947-2 125/63 200/200 400V Icu/Ics...
  • Page 33 Frame (A) 1000 Type NF1000-SS Rated current In (A) 500-600-700-800-900-1000 Rated insulation voltage Ui (V) AC 25/13 690V AC Breaking 65/33 500V capacity (kA rms) 85/43 440V IEC60947-2 85/43 400V Icu/Ics 125/63 230V Number of poles Standard Solid-state Automatic tripping Adjustable ampere rating device Adjustable short time delay pick up...
  • Page 34 Frame (A) 1250 Type NF1250-SS Rated current In (A) 600-700-800-1000-1200-1250 Rated insulation voltage Ui (V) AC 25/13 690V AC Breaking 65/33 500V capacity (kA rms) 85/43 440V IEC60947-2 85/43 400V Icu/Ics 125/63 230V Number of poles Standard Solid-state Automatic tripping Adjustable ampere rating device Adjustable short time delay pick up...
  • Page 35 Frame (A) 1250 Type NF1250-UR Rated current In (A) 600-700-800-1000-1200-1250 Rated insulation voltage Ui (V) AC – 690V AC Breaking 85/42 500V capacity (kA rms) 125/65 440V IEC60947-2 125/65 400V Icu/Ics 170/85 240V Number of poles Standard Solid-state Automatic tripping Adjustable ampere rating device Adjustable short time delay pick up...
  • Page 36 Frame (A) 1600 Type NF1600-SS Rated current In (A) 800-1000-1200-1400-1500-1600 Rated insulation voltage Ui (V) AC 25/13 690V AC Breaking 65/33 500V capacity (kA rms) 85/43 440V IEC60947-2 85/43 400V Icu/Ics 125/63 230V Number of poles Standard Solid-state Automatic tripping Adjustable ampere rating device Adjustable short time delay pick up...
  • Page 37 Frame (A) 2000 2500 Type NF2000-S NFE2000-S NF2500-S Rated current In (A) 1200-1400-1600-1800-2000 1800, 2000 2500 Rated insulation voltage Ui (V) AC – – – 600V AC Interrupting 65/50 65/50 65/50 500V capacity (kA rms) 85/50 85/50 85/50 415V IEC157-1 85/50 85/50 85/50...
  • Page 38 Frame (A) 3000 (3200) NFE3000-S Type NF3200-S Rated current In (A) 2800, 3000, 3200 1800-2000-2500-3000 Rated insulation voltage Ui (V) AC – – 600V AC Interrupting 65/50 500V 65/50 capacity (kA rms) 85/50 415V 85/50 IEC157-1 85/50 85/50 380V P1/P2 125/85 240V 125/85...
  • Page 39 Frame (A) 4000 NFE4000-S Type NF4000-S Rated current In (A) 3600, 4000 2500-3000-3500-4000 Rated insulation voltage Ui (V) AC – – 600V AC Interrupting 65/50 500V 65/50 capacity (kA rms) 85/50 415V 85/50 IEC157-1 85/50 85/50 380V P1/P2 125/85 240V 125/85 Number of poles Standard...

  • Page 40: Protective Co-Ordination

    The advantage of the cascade back-up approach is that it facilitates the use of low cost, low fault level breakers downstream, thereby offering savings in both the cost and size of equipment. As Mitsubishi MCCBs have a very considerable current limiting effect, they can be used to provide this ‘cas- cade back-up’ protection for downstream circuit breakers.

  • Page 41: Interrupting Capacity Consideration

    6.2 Interrupting Capacity Consideration Table 1 230VAC 3ph trans. 50~75 150~300 30 or less 500~1500 2000~3000 capacity (kVA) 1ph trans. – 20 or less 100~150 30~50 200~500 capacity (kVA) Interrupting capacity 170 200 (kA)(sym) NF30- NF30- NF50-CP 50·60 NF50-HP, NF60-HP NF50-HRP NF60-CP NF100-HP...

  • Page 42: Selective-Interruption

    6.3 Selective-Interruption (Discrimination) Main breaker 6.3.1 Selective-Interruption Combination Continuous supply Following tables show combinations of main-circuit selective coordination breakers and branch breakers and the available selective tripping current at the set- ting points at the branch-circuits. Branch breaker Short-circuit point Healthy circuit Selection Conditions 1.
  • Page 43 Selective interruption combinations (MCCB-MCCB) 230VAC (Sym. kA) Main Breaker Branch Breaker Icu(kA) NF30-SP NF50-HP NF60-HP NF50-HRP – – NF100-SP NF100-SP T/A – – NF100-SEP NF100-HP NF100-HP T/A – – NF100-HEP NF160-SP – – – – NF160-SP T/A NF250-SP – – –...
  • Page 44 Selective interruption combinations 440VAC (Sym. kA) Main Breaker Branch Breaker Icu(kA) NF30-SP NF50-HP NF60-HP NF50-HRP – – NF100-SP NF100-SP T/A – – NF100-SEP NF100-HP NF100-HP T/A – – NF100-HEP NF160-SP – – – – NF160-SP T/A NF250-SP – – – –...
  • Page 45 Selective interruption combinations (ACB-MCCB) 230VAC (Sym. kA) Main Breaker AE630-SS AE1000-SS AE1250-SS AE1600-SS AE2000-SS AE2500-SS AE3200-SS AE4000-SSC Ics(kA) (kA) Branch Breaker NF100-CP 15(25) NF100-SP 16(50) 45(50) NF100-SP T/A 16(50) 45(50) NF100-HP 24(65) NF100-HP T/A 24(65) NF100-SEP 16(50) NF100-HEP 24(65) NF160-SP 15(50) 24(50) 30(50)
  • Page 46 440VAC (Sym. kA) Main Breaker AE630-SS AE1000-SS AE1250-SS AE1600-SS AE2000-SS AE2500-SS AE3200-SS AE4000-SSC Ics(kA) (kA) Branch Breaker NF100-CP 9.8(10) NF100-SP 9(30) 20(30) 25(30) NF100-SP T/A 9(30) 20(30) 25(30) NF100-HP 16(50) NF100-HP T/A 16(50) NF100-SEP 9(25) 20(25) NF100-HEP 16(50) NF160-SP 7(25) 14(25) 19(25) NF160-SP T/A...

  • Page 47: Cascade Back-Up Protection

    6.4 Cascade Back-up Protection 6.4.1 Cascade Back-up Combinations Main breaker Following tables show the available MCCB combina- tions for cascade interruption and their interrupting capacity. Branch Branch breaker breaker Fault point 440VAC Main MCCB Branch MCCB 25 50 25 50 25 50 42 65 125 42 65 125 42 65 125 85 85 85 15 25 36 36 125 200 125 200 200 200 200 125 NF30-SP 2.5 10 14 5 5 5 5 –...
  • Page 48 230VAC Main MCCB Branch MCCB 50 100 50 100 50 100 85 100 125 85 100 125 85 100 125 125 125 125 30 50 50 50 125 200 125 200 200 200 200 170 NF30-SP 5 42 50 10 10 10 10 – – – – – – – – – – – – 7.5 – – – 125 200 35 50 – – – – MB30-SP MB50-CP 42 85 35 35 35 35 30 30 30 30 30 30 –...

  • Page 49: Limiting Characteristics

    6.5 I t let-Through and Current Limiting Characteristics (440 VAC) t let-through characteristics Current limiting characteristics ( 10 NF100-HP,NF250-HP NF100-HP,NF250-HP NF250-HP NF250-HP NF100-HP (40~100A) NF100-HP(30A) NF100-HP(20A) NF100-HP (40~100A) NF100-HP(15A) NF100-HP (30A) NF100-HP (20A) NF100-HP (15A) 60 80 100 60 80 100 short-circuit current,sym.r.m.s.(kA) short-circuit current,sym.r.m.s.(kA) ( 10...

  • Page 50: Protective Coordination With Wiring

    Allowable I t=14000S 6.6 Protective Coordination with Wiring Considering let-through energy (∫i dt) in a fault where 6.6.1 General Considerations the protector has no current-limiting capability, if short- If it is assumed that the heat generated by a large circuit occurs when let-through current is max., ∫i current passing through a wire is entirely dissipated within the wire, the following expression is applicable 1 cycle interruption...
  • Page 51 1000 Wire sizes (mm 0.4 0.5 0.6 30 40 50 1000 Current (×10 Fig. 6.14 Relation of Let-through Current to Time until 600V Vinyl-Insulated Wire Reaches a 70°C Temperature Rise. (In a Start from No Load State at Ambient Temperature of 30°C) ground use;...
  • Page 52 2000 2000 1000 1000 Wire size Wire size 1.0mm 1.5mm 10mm 2.5mm 16mm 4.0mm 25mm 6.0mm MCCB rating MCCB rating 100A 1000 10000 1000 10000 Current (A) Current (A) a) 50A-fream MCCB b) 100A-fream MCCB 2000 2000 1000 1000 Wire size Wire size 16mm 50mm...

  • Page 53: Protective Coordination With Motor Starters

    6.7 Protective Coordination with Motor Starters full-load current without destruction of its heater ele- ment. Mitsubishi Type TH OLRs are normally capable Motor starters comprise a magnetic contactor and a of handing 12 to 20 times rated current; in addition...
  • Page 54 0.3 at starting, causing a significant DC component, degree of sacrifice of protection. Mitsubishi provides so that the total transient inrush current may reach a unique solution to this problem in the form of a satu- about twice the value of the AC component, even rable reactor added to the OLR heater element.

  • Page 55: Coordination With Devices On The High-Voltage Circuit

    Thus, if normal starting current is assumed as 600% of full-load current, the peak inrush becomes 1200% in Y-delta restarting and 1600% in direct restarting. The MCCB instantaneous-trip setting must be selected at larger than these values. Fig. 6.21 shows test date with respect to four condi- tions of transient inrush current, expressed as magni- fications of full-load current, measured on motors rated from 0.2~30kW.
  • Page 56 OCR dial is normally set to 0.2 or less, or 1 second max. if it has an instantaneous trip element. On the Mitsubishi Type MOC-E general-purpose relay this is equivalent to dial setting No. 2. Latching-curve over- lap, shown by the broken lines in Fig. 6.27, must be allowed for.
  • Page 57 can be seen from Fig. 6.27 that the maximum trip curve (tolerance) of the C Line units matches well with the NF800-SEP curves, with no danger of overlap. NF800-SEP NF250-CP 800A setting 175A 10 min MOC-E tripping curve Max. CT ratio 150/5 Dial Min.

  • Page 58: Selection

    7.1.2 Motor Breaker Ambient Where starting times are relatively short and currents conditions are small, the Mitsubishi M Line motor breakers can Installation and be used without the need for a motor starter. connection style Wire 7.2 For Lighting and Heating Branch Cir-...

  • Page 59: For Main Circuit

    7.3 For Main Circuits W = I and average heat produced: 7.3.1 For Motor Loads I Rt The method of “synthesized motors” is recommended β ) Rβ = R(I – that is, the branch-circuit loads to be connected are where β is the duty factor, defined as divided into groups of motors to be started simulta- neously (assumed), and then each group is regarded total conduction time...
  • Page 60 comes: 7.4.2 MCCB Instantaneous Trip and Trans- rated capacity former Excitation Surge duty factor When a welding-transformer primary circuit is closed, rated voltage 85 + 10 depending upon the phase angle at the instant of clo- 0.5 = 300A sure, a transient surge current will flow, due to the super-imposed DC component and the saturation of Hence, the MCCB rated current becomes: the transformer core.

  • Page 61: For Transformer-Primary Use

    for 2 minutes. Thus: The total, 2f , represents an excitation current in excess of the saturation value. The decay-time con- 1.2 x P x 10 ≥ MCCB stant of this tends to be larger for larger transformer capacities. Table 7.2 shows typical values of excita- where 1.2: Allowance for random variations in tion surge current, but as these do not take circuit arc-welder current, and supply-volt-...

  • Page 62: For Capacitor Circuits

    Fig. 7.10 Accumulative Capacitor Charge be completed. Since Mitsubishi MCCBs exhibit extremely rapid When the switch (Fig. 7.11) is closed, a charge contact separation, repetitive arcing is virtually non- (q=CV) must be instantaneously supplied to equal the...

  • Page 63: For Thyristor Circuits

    under the application of the above current, but selec- instantaneous supply voltage (V), according to the tion of an MCCB with an instantaneous-trip current of phase angle at the instant of circuit closure. This 6200 greater than = 4400A is recommended for an charge results in a large surge current.
  • Page 64 Table 7.4 MCCB Selection for Circuits with PF-Correction a) 230V, 50Hz Circuit c) 400V, 50Hz Circuit Capacitor rating Single-phase circuit Three-phase circuit Capacitor rating Single-phase circuit Three-phase circuit Capacitor MCCB Capacitor MCCB Capacitor MCCB Capacitor MCCB rated rated rated rated rated rated rated...
  • Page 65 Fault element MCCB1 MCCB2 Fig. 7.13 AC- and DC-side Protectors for Thyristors Fig. 7.14 Fault-Current Flow Table 7.5 Thyristor Circuits and Current Formats Circuit No. I Circuit No. II Circuit No. III Circuit No. IV MCCB1 MCCB1 MCCB1 MCCB1 Circuit diagram MCCB2 MCCB2 Load...
  • Page 66 tates rapid interruption of the circuit. Normally, such protection (MCCB1, Fig. 7.15) is presented, but the interruption takes place within one cycle; thus, from DC-protection case (MCCB2) can be plotted in the the point of view of element thermal destruction, the same way.
  • Page 67 3-Phase Fullwave Rectification MCCB : Mag-Only Overcurrent-relay High-speed current-limiting fuse MCCB tripping Thyristor current-surge withstand Region 1 0.05 Region 3 0.02 Region 2 0.01 300 400 500 600 700 1000 1500 2000 3000 4000 Current (% of rating) Fig. 7.17 Thyristor and Protector Operating Curves 3.
  • Page 68 Fig. 7.19 shows connection of high-speed fuses rent. For MCCB selection, the latter types can be re- for protection against thyristor breakdown that would garded as lighting and heating general loads, as pre- otherwise result in short-circuit flow from the AC sup- viously discussed.

  • Page 69: Selection Of Mccbs In Inverter Circuit

    7.8 Selection of MCCBs in inverter circuit 7.8.1 Cause of distorted-wave current Distorted-wave current is caused by factors such as the CVCF device of a computer power unit, various recti- fiers, induction motor control VVVF device corresponding to more recent energy-saving techniques, etc, wherein thyristor and transistor are used.
  • Page 70 Table 7.9 Data of High Harmonic Wave Current Content in Inverter Power Circuit (Example) High harmonic wave current content (%) High harmonic P W M P A M wave degree No ACL (Standard) With power factor modifying ACL With standard ACL With power factor modifying ACL Basic 81.6...

  • Page 71: Environmental Characteristics

    8. ENVIRONMENTAL CHARACTERISTICS 8.1 Atmospheric Environment 8.1.1 High Temperature Application To comply with relevant standards, all circuit break- Abnormal environments may adversely affect perfor- ers are calibrated at 40˚C. If the circuit breaker is to mance, service life, insulation and other aspects of be used in an environment where the ambient tem- MCCB quality.

  • Page 72: Vibration-Withstand Characteristics

    In conditions where temperatures reach as low as The derating factors that are applicable for high alti- –5˚C special MCCBs are usually required. Mitsubishi, tude applications are shown in table 8.3. (According however, have tested their standard MCCBs to tem- to ANSI C 37.29-1970)

  • Page 73: Shock-Withstand Characteristics

    • A case the switched condition changed from ON to OFF • A case the switched condition changed from ON to Trip • A case the sample shows physical damage Table 8.4 Shock-Withstand Characteristics of Mitsubishi MCCB No tripped No damage Series Type...

  • Page 74: Short-Circuit Current Calculations

    9. SHORT-CIRCUIT CURRENT CALCULATIONS 9.1 Purpose the MCCB, generally, the short-circuit current is cal- culated from the impedance on the supply side of the Japanese and international standards require, in sum- breaker. mary, that an overcurrent protector must be capable Fig.
  • Page 75 Table 9.1 Impedances of 3-Phase Transformers MCCB Impedance (%) Transformer Load capacity (kVA) Supply side 1.81 1.31 Load terminal in the case of 1.78 1.73 insulated line (the line impedance on the MCCB 1.73 1.74 load side can be added.) 1.61 1.91 1.63...
  • Page 76 Thus, when calculating the short-circuit current at ) · Z various points in a load system, if the value Z is first + j X computed, it is a simple matter to add the various wire ) {R ) – X or bus-duct impedances.

  • Page 77: Classification Of Short-Circuit Current

    9.4 Classification of Short-Circuit Current 2πR 2πR – – · { 1 + 2e + 2 1 + } = I · K A DC current (Fig. 9.3) of magnitude determined by the voltage phase angle at the instant of short circuit 2πR 2πR –...

  • Page 78: Calculation Procedures

    9.5 Calculation Procedures Table 9.5 Necessary Equations Ohmic method % impedance method Remarks · Z x 100 ....Eq. 2 %Z = x 100 ......Eq. 1' M3 · V · %Z V/M3 ........Eq. 1 M3 · Z = M3 · V · I .......Eq.
  • Page 79 Table 9.6 Calculation Example: 3-Phase Short-Circuit Current % impedance method Ohmic method The supply short-circuit capacity, being unknown, is The supply short-circuit capacity, being unknown, is defined as 1000MVA with X = 25. defined as 1000MVA with X = 25. From Eq.
  • Page 80 MOULDED CASE CIRCUIT BREAKERS Safety Tips Be sure to read the instruction manual fully before using this product. HEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310. TELEX: J24532 CABLE: MELCO TOKYO Made from recycled paper Revised publication, effective July. 2000 Y-0525-C 0007 (ROD) Printed in Japan Specifications subject to change without notice.

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